1. Field of the Invention
The present invention relates to an image processing apparatus. More specifically, the present invention relates to an apparatus and a program for obtaining processed compressed moving image data by carrying out image enhancement processing on compressed moving image data.
2. Description of the Related Art
For attractive moving-image display, processing such as gradation correction for improving image quality (hereinafter referred to as image enhancement processing) is carried out on a moving image obtained by photography. In Japanese Patent No. 3087409, a method is proposed for gradation correction. In this method, a video signal such as an NTSC signal is firstly subjected to A/D conversion to generate moving image data. A brightness histogram is then calculated regarding the moving image data, and a look-up table based on the histogram is generated and used for gradation correction.
Meanwhile, following the spread of digital cameras and camera-embedded mobile phones recently, a moving image is often dealt with as a video signal such as an NTSC signal as well as digitally compressed data according to a compression standard such as MPEG. Unlike photography of a still image, flash is difficult to use for a moving image. Therefore, a moving image photographed by an imaging device such as a digital camera tends to be dark. In order to display a moving image comprising image data having been subjected to digital compression, image enhancement processing is necessary as in the case of an analog signal such as an NTSC signal.
Such moving image data are recorded in a recording medium and sent in a state of being compressed. Therefore, a device for displaying the moving image data needs to carry out display processing on the moving image data on the premise that the moving image data have been compressed. Consequently, processed image data generated by image enhancement processing on the compressed moving image data need to be compressed according to the display device.
However, in order to obtain processed compressed moving image data through image enhancement processing, moving image data compressed digitally according to a compression standard such as MPEG (hereinafter referred to as compressed moving image data) are decoded first. The decoded data are then subjected to image enhancement processing. Thereafter, the corrected (enhanced) data are encoded to generate processed compressed moving image data. Since decoding and encoding moving image data requires a large amount of operations, this is time-consuming processing. This problem of long processing time is also noticed in the field of communication.
In the field of mobile communication as one form of communication, mobile terminals such as mobile phones have spread widely, and functions thereof have been improved. Consequently, services related to images are provided for such mobile terminals. For example, some communication relay servers have an image enhancement function. When an e-mail is relayed from a sender mobile phone to a receiver mobile phone, such a server carries out image enhancement processing such as gradation correction, white balance correction, density correction, and sharpness processing on image data attached to the e-mail sent from the sender mobile phone. Thereafter, the server sends the image data to the receiver mobile phone, or temporarily stores the image data for future downloading. If the image enhancement processing is not carried out fast in the server, a user feels stressful. Therefore, the service is not improved but degraded. Furthermore, if the time necessary for the image enhancement processing is long, the server needs to have a large-capacity storage device for storing the image data to be processed. In this manner, the server becomes more costly.
The same phenomenon is also observed in the field of video phones. If image enhancement processing cannot be carried out fast, a user cannot view an image of his/her counterpart in real time. Therefore, such a video phone becomes meaningless, and communication is not carried out smoothly.
This problem is also observed in other fields. For example, in the case where moving image data recorded in a recording medium such as a CD-ROM are displayed on a monitor of a computer, the computer carries out image enhancement processing for appropriate display of a moving image. However, if the image enhancement processing is prolonged, a user feels stressful as in the case of communication.